<p>Because <code>printf</code>-style format strings are interpreted at runtime, rather than validated by the compiler, they can contain errors that
result in the wrong strings being created. This rule statically validates the correlation of <code>printf</code>-style format strings to their
arguments when calling the <code>format(...)</code> methods of <code>java.util.Formatter</code>, <code>java.lang.String</code>,
<code>java.io.PrintStream</code>, <code>MessageFormat</code>, and <code>java.io.PrintWriter</code> classes and the <code>printf(...)</code> methods of
<code>java.io.PrintStream</code> or <code>java.io.PrintWriter</code> classes. </p>
<h2>Noncompliant Code Example</h2>
<pre>
String.format("First {0} and then {1}", "foo", "bar");  //Noncompliant. Looks like there is a confusion with the use of {{java.text.MessageFormat}}, parameters "foo" and "bar" will be simply ignored here
String.format("Display %3$d and then %d", 1, 2, 3);   //Noncompliant; the second argument '2' is unused
String.format("Too many arguments %d and %d", 1, 2, 3);  //Noncompliant; the third argument '3' is unused
String.format("First Line\n");   //Noncompliant; %n should be used in place of \n to produce the platform-specific line separator
String.format("Is myObject null ? %b", myObject);   //Noncompliant; when a non-boolean argument is formatted with %b, it prints true for any nonnull value, and false for null. Even if intended, this is misleading. It's better to directly inject the boolean value (myObject == null in this case)
String.format("value is " + value); // Noncompliant
String s = String.format("string without arguments"); // Noncompliant

MessageFormat.format("Result '{0}'.", value); // Noncompliant; String contains no format specifiers. (quote are discarding format specifiers)
MessageFormat.format("Result {0}.", value, value);  // Noncompliant; 2nd argument is not used
MessageFormat.format("Result {0}.", myObject.toString()); // Noncompliant; no need to call toString() on objects

java.util.Logger logger;
logger.log(java.util.logging.Level.SEVERE, "Result {0}.", myObject.toString()); // Noncompliant; no need to call toString() on objects
logger.log(java.util.logging.Level.SEVERE, "Result.", new Exception()); // compliant, parameter is an exception
logger.log(java.util.logging.Level.SEVERE, "Result '{0}'", 14); // Noncompliant - String contains no format specifiers.
logger.log(java.util.logging.Level.SEVERE, "Result " + param, exception); // Noncompliant; Lambda should be used to differ string concatenation.

org.slf4j.Logger slf4jLog;
org.slf4j.Marker marker;

slf4jLog.debug(marker, "message {}");
slf4jLog.debug(marker, "message", 1); // Noncompliant - String contains no format specifiers.

org.apache.logging.log4j.Logger log4jLog;
log4jLog.debug("message", 1); // Noncompliant - String contains no format specifiers.
</pre>
<h2>Compliant Solution</h2>
<pre>
String.format("First %s and then %s", "foo", "bar");
String.format("Display %2$d and then %d", 1, 3);
String.format("Too many arguments %d %d", 1, 2);
String.format("First Line%n");
String.format("Is myObject null ? %b", myObject == null);
String.format("value is %d", value);
String s = "string without arguments";

MessageFormat.format("Result {0}.", value);
MessageFormat.format("Result '{0}'  =  {0}", value);
MessageFormat.format("Result {0}.", myObject);

java.util.Logger logger;
logger.log(java.util.logging.Level.SEVERE, "Result {0}.", myObject);
logger.log(java.util.logging.Level.SEVERE, "Result {0}'", 14);
logger.log(java.util.logging.Level.SEVERE, exception, () -&gt; "Result " + param);

org.slf4j.Logger slf4jLog;
org.slf4j.Marker marker;

slf4jLog.debug(marker, "message {}");
slf4jLog.debug(marker, "message {}", 1);

org.apache.logging.log4j.Logger log4jLog;
log4jLog.debug("message {}", 1);
</pre>
<h2>See</h2>
<ul>
  <li> <a href="https://www.securecoding.cert.org/confluence/x/wQA1">CERT, FIO47-C.</a> - Use valid format strings </li>
</ul>

